In the criminal justice (CJ) system in the US, there are high rates of mental health and substance use disorders. Although prisons must provide treatment, the CJ system is resource-poor and the presenting problems of prisoners are diverse. To maximize efficiency in the CJ context, recent efforts focus adjunctive interventions on symptoms that are most detrimental to prisoners, and that are shared across diverse conditions. Of particular interest has been anger dysregulation, as this is prevalent in CJ-involved populations, contributing not only to distress and exacerbation of other mental health problems, but also to risk of aggression. Overt aggression further increases risk for prison behavioral infractions or placement in restraints or seclusion, and may delay parole or release decisions. There are many limitations to existing approaches to anger management in prison. We propose that hatha yoga could serve as a useful adjunctive treatment for anger within prisons. In addition to preliminary research showing that yoga programs may improve anger regulation, research has also demonstrated benefits of yoga for related symptoms of depression, anxiety, and trauma-related emotion reactivity and arousal. Yoga may be delivered in a relatively low-cost fashion. Finally, prisoners may view yoga as less stigmatizing than more traditional anger management interventions, particularly given its focus on physical body awareness/movement and on overall wellness. Despite a recent proliferation of yoga programs for various problems in prisons, empirical research on this topic is minimal, with a small number of studies limited by significant methodological concerns. We propose to conduct systematic treatment development research that would prepare us to study whether yoga (vs. a health education control group) is an effective adjunctive treatment for prisoners with anger dysregulation. In Phase 1 (Treatment Development Stage 1A) of the proposed project, we will refine our current manualized Hatha yoga intervention and health education intervention for specific use with prisoners with high levels of anger dysregulation. We will conduct focus groups with prisoners and prison administrators, and solicit feedback from relevant experts, in order to make modifications to our yoga and health education treatment manuals. In Phase 2 (Treatment Development Stage 1B), we will conduct a pilot randomized clinical trial (n = 40) of Hatha yoga vs. a health education group (attention control) for prisoners high in self-reported anger dysregulation. Participants will be enrolled in the active intervention for 10 weeks, and then followed for 8 weeks. We will assess feasibility and acceptability of the yoga program, the health education control group, and research procedures. To assess safety, we will track all adverse events in a structured fashion. We do not expect to see any serious adverse events definitely or probably related to study participation. We will iteratively revise manuals and materials, making final revisions at the end of the pilot RCT. If successful, this project will provide us with materials, experience, and pilot data needed for the next stage of this line of research, namely, a fully powered RCT.